View source for Cob (material)

{{Short description|Building material made of soil and fiber}}
[[File:Cob wall mud construction.jpg|upright|thumb|Building a wall out of cob]]
'''Cob''', '''cobb''', or '''clom''' (in Wales) is a natural [[building material]] made from [[subsoil]], water, fibrous [[organic material]] (typically [[straw]]), and sometimes [[Lime (material)|lime]].<ref>Wright, Joseph. "COB(B, sb3. 1.", ''The English Dialect Dictionary, Being the Complete Vocabulary of All Dialect Words Still in Use, or Known to Have Been in Use during the Last Two Hundred Years''. London: H. Frowde;, 1898. 676-677. Print.</ref> The contents of subsoil vary, and if it does not contain the right mixture, it can be modified with sand or clay. Cob is fireproof, termite proof, resistant to seismic activity,<ref>{{cite news |last=Goodnow |first=Cecelia |title=Thinking of building a cob home?|url=http://www.seattlepi.com/lifestyle/article/Thinking-of-building-a-cob-home-1251753.php |newspaper=Seattle Post-Intelligencer|date=October 5, 2007}}</ref> and uses low-cost materials, although it is very labour intensive. It can be used to create artistic and sculptural forms, and its use has been revived in recent years by the natural building and [[sustainability]] movements.

In technical building and engineering documents, such as the [[Uniform Building Code]] of the western USA, cob may be referred to as "unburned clay masonry," when used in a structural context. It may also be referred to as "aggregate" in non-structural contexts, such as "clay and sand aggregate," or more simply "organic aggregate," such as where cob is a filler between [[Timber framing|post and beam]] construction.

==History and usage==
[[File:Cob stitch copy.jpg|thumb|"Cob stitch" repair on old traditional cob cottage in [[Devon]], England]]
[[File:Maison de Jeanne, Sévérac-le-Château.jpg|thumb|[[Maison de Jeanne]], Sévérac-le-Château. Timber and cob construction]]
''Cob'' is an English term attested to around the year 1600<ref>"cob, n2. 1." ''Oxford English Dictionary'' 2nd. ed. 2009. CD-rom.</ref> for an ancient building material that has been used for building since prehistoric times. The use of this material in Iran is more than 4000 years old. The etymology of ''cob'' and ''cobbing'' is unclear, but in several senses means to ''beat'' or ''strike'',<ref>{{cite web|title=cob |url=https://www.collinsdictionary.com/dictionary/english/cob |website=Collins English Dictionary|publisher=HarperCollins|access-date=13 January 2017|quote=verb: ''(transitive) British informal'' to beat, esp on the buttocks}}</ref> which is how cob material is applied to a wall.

Many similar materials and methods of earthen building are used around the world, such as ''[[adobe]]'',<ref name=Rapp>Rapp, George Robert. "Unbaked clay or mud", ''Archaeomineralogy''. 2nd ed. Berlin: Springer, 2009. Print.</ref> ''lump clay'',<ref name=Rapp/> ''[[Puddling (engineering)|puddled]] clay'', ''chalk mud'',<ref name=Rapp/> ''[[wychert]]'',<ref name=Rapp/> ''clay daubins'',<ref name=Rapp/> ''swish'' ([[Asante Twi]]),<ref>{{cite web|last1=Oliver|first1=Paul|last2=Hess|first2=Janet B.|title=African architecture|url=https://www.britannica.com/art/African-architecture#ref519949|website=Encyclopædia Britannica|access-date=13 January 2017|date=23 February 2012}}</ref> ''torchis'' (French),<ref name=CL>Edwards, Jay Dearborn, and Nicolas Verton. "mud with straw", ''A Creole Lexicon Architecture, Landscape, People''. Baton Rouge: Louisiana State UP, 2004. Print.</ref> ''bauge'' (French),<ref name=CL/> ''bousille'' (French mud with moss),<ref name=CL/> beaten clay-''pahsa'' (Central Asia), and ''cat and clay''.<ref>[http://www.merriam-Webster.com/dictionary/cat%20and%20clay "cat and clay" Websters Online Dictionary accessed March 23, 2015.]</ref>

Cob structures can be found in a variety of climates across the globe. European examples include:

* in England, notably in the counties of [[Devon]] and [[Cornwall]] in the [[West Country]], and in [[East Anglia]] (where it is referred to as ''clay lump'')<ref>{{cite web|last1=Bouwens|first1=Dirk|title=Earth Buildings and Their Repair|url=https://www.buildingconservation.com/articles/earth/earth_buildings.htm |website=buildingconservation.com |publisher=Cathedral Publications Ltd.|access-date=13 January 2017}} ''[reproduced from The Building Conservation Directory, 1997]''</ref>
* in Wales, notably in rural [[Anglesey]]<ref>{{cite book|title=The Architecture of Wales From the First to the Twenty-First Century|page=13|year=2018|last=Hilling|first=John B.|publisher=University of Wales Press|isbn= 9781786832856}}</ref>
* in [[Donegal Bay]] in [[Ulster]] and in Munster, South-West [[Ireland]]{{citation needed|date=July 2016}}
* in [[Finistère|Finisterre]] and Ille-et-Vilaine in [[Brittany]], where many homes have survived over 500 years and are still inhabited{{citation needed|date=September 2010}}

Some of the oldest human-made structures in Afghanistan are composed of [[rammed earth]] and cob.<ref>{{cite news |last=McArdle |first=Patricia |title=Afghanistan's Last Locavores |url=https://www.nytimes.com/2011/06/20/opinion/20mcardle.html?_r=2 |newspaper=[[The New York Times]] |date=June 19, 2011}}</ref> Cobwork (''tabya'') was used in the [[Maghreb]] and [[al-Andalus]] in the 11th and 12th centuries, and was described in detail by [[Ibn Khaldun]] in the 14th century.<ref>{{cite book |last=Routledge Hill |first=Donald |author-link=Donald Routledge Hill |editor1-last=Rashed |editor1-first=Roshdi |editor2-last=Morelon |editor2-first=Régis |year=1996 |chapter=Engineering |title=Encyclopedia of the history of Arabic science |volume=3 |isbn=0-415-02063-8 |page=766}}</ref>

Many old cob buildings can be found in [[Africa]], the Middle East, and the southwestern United States like the [[Taos Pueblo]].{{citation needed|date=September 2010}} A number of cob cottages survive from mid-19th-century New Zealand.<ref name=NZHPT>Dozens of cob cottages are [http://www.historic.org.nz/TheRegister/RegisterSearch/SearchResults.aspx?s=s&NameOrID=cob listed on the Register] of the New Zealand Historic Places Trust, e.g. {{cite web|title=Ferrymead Cob Cottage|url=https://www.heritage.org.nz/the-list/details/3101|work=Rarangi Taonga: the Register of Historic Places, Historic Areas, Wahi Tapu and Wahi Tapu Areas|publisher=New Zealand Historic Places Trust Pouhere Taonga|access-date=21 August 2013}}</ref>

Traditionally, English cob was made by mixing the clay-based subsoil with sand, straw and water using [[oxen]] to trample it. English soils contain varying amounts of [[chalk]], and cob made with significant amounts of chalk are called ''chalk cob'' or ''[[wychert]]''. The earthen mixture was then ladled onto a stone [[Foundation (architecture)|foundation]] in [[Course (architecture)|courses]] and trodden onto the wall by workers in a process known as ''cobbing''. The construction would progress according to the time required for the prior course to dry. After drying, the walls would be trimmed and the next course built, with lintels for later openings such as doors and windows being placed as the wall takes shape.<ref name="SnellCallahan2009">{{cite book |last1=Snell |first1=Clarke |last2=Callahan |first2=Tim |title=Building Green: A Complete How-to Guide to Alternative Building Methods : Earth Plaster, Straw Bale, Cordwood, Cob, Living Roofs |url= https://books.google.com/books?id=gGEbRyok6f0C&pg=PA276 |access-date=1 June 2013 |year=2009 |publisher=Sterling Publishing Company, Inc. |isbn=978-1-60059-534-9 |pages=276–}}</ref>

The walls of a cob house are generally about {{convert|24|in|cm}} thick, and windows were correspondingly deep-set, giving the homes a characteristic internal appearance. The thick walls provided excellent [[thermal mass]] which was easy to keep warm in winter and cool in summer. Walls with a high thermal mass value act as a thermal buffer inside the home.<ref>{{cite journal |last1=Goodhew |first1=Steven |last2=Griffiths |first2=Richard |year=2005 |title=Sustainable earth walls to meet the building regulations |journal=Energy and Buildings |volume=37 |issue=5 |page=1 |publisher=Elsevier |doi=10.1016/j.enbuild.2004.08.005 |bibcode=2005EneBu..37..451G |url=http://gse.cat.org.uk/downloads/Goodhew,_2005.pdf |access-date=24 January 2013 |archive-url=https://web.archive.org/web/20150110000828/http://gse.cat.org.uk/downloads/Goodhew,_2005.pdf |archive-date=10 January 2015 |url-status=dead }}</ref> The material has a long life-span even in rainy or humid climates, provided a tall foundation and large roof overhang are present

Cob is [[fireproof]],<ref>{{Cite journal |last=Cioruța |first=Bogdan |date=2016 |title=Trends In The Techniques Of Design And Building Traditional Earth Houses |url=https://www.proquest.com/docview/1856858074 |journal=Scientific Bulletin Series D: Mining, Mineral Processing, Non-Ferrous Metallurgy, Geology and Environmental Engineering |publisher=[[North University of Baia Mare]] |volume=30 |issue=2 |pages=21–31 |id={{ProQuest|1856858074}} |via=ProQuest}}</ref>{{Rp|page=28}} while "fire cob" (cob without straw or fiber) is a [[refractory material]] (the same material, essentially, as unfired common red brick), and historically, has been used to make chimneys, fireplaces, forges and crucibles. Without fiber, however, cob loses most of its tensile strength.<ref>{{Cite journal |last=Saxton |first=R. H. |date=1995 |title=The performance of cob as a building material |url=https://www.istructe.org/journal/volumes/volume-73-(published-in-1995)/issue-7/the-performance-of-cob-as-a-building-material/ |journal=The Structural Engineer |publisher=[[The Institution of Structural Engineers]] |volume=73 |issue=7 |pages=111–15}}</ref>{{Rp|page=114}}

==Modern cob buildings==
[[File:Home at Hollyhock.jpg|thumb|250px|An example of a modern cob building in the Pacific Northwest style. The exterior cob wall is limewashed for an attractive, uniform appearance.]]
[[File:Sota Construction Office Building.jpg|thumb|left|alt=The Sota Construction Services Corporate Headquarters in [[Pittsburgh]], [[Pennsylvania]], [[United States]], constructed of cob walls|The Sota Construction Services Corporate Headquarters in [[Pittsburgh]], [[Pennsylvania]], [[United States]], constructed of cob walls]]
[[File:Beautifying cob oven.jpg|thumb|250px|Decorating a cob oven]]When Kevin McCabe constructed a two-story, four bedroom cob house in [[England]], [[UK]] in 1994, it was reputedly the first cob residence built in the country in 70 years. His techniques remained very traditional; the only innovations he made were using a [[tractor]] to mix the cob and adding sand or shillet, a gravel of crushed [[shale]], to reduce shrinkage.{{citation needed|date=July 2016}}

[[File:The Cob House - Cadhay.jpg|thumb|left|A modern cob house near [[Ottery St Mary]], [[United Kingdom]]]] From 2002 to 2004, sustainability enthusiast [[Rob Hopkins]] initiated the construction of a cob house for his family, the first new one in [[Ireland]] in circa one hundred years. It was a community project, but an unidentified [[arsonist]] destroyed it shortly before completion.<ref>[http://transitionculture.org/about/ Practical Sustainability: About]</ref> The house, located at The Hollies Centre for Practical Sustainability in [[County Cork]], was being rebuilt as of 2010. There are a number of other completed modern cob houses and more are planned, including a public education centre.<ref>{{cite web |author=Welcome to The Hollies |url=http://thehollies.ie |title=The Hollies |publisher=thehollies.ie |date=2010-08-03 |access-date=2010-12-04}}</ref>

In 2000-01, a modern, four bedroom cob house in [[Worcestershire]], [[England]], [[UK]], designed by [[Associated Architects]], was sold for £999,000. Cobtun House was erected in 2001 and won the [[Royal Institute of British Architects]]' Sustainable Building of the Year award in 2005. The total construction cost was £300,000, but the metre (yard) thick outer cob wall cost only £20,000.{{citation needed|date=July 2016}}

In the Pacific Northwest of the [[United States]] there has been a resurgence of cob construction, both as an alternative building practice and one desired for its form, function, and cost effectiveness. Pat Hennebery, Tracy Calvert, Elke Cole, and the Cobworks workshops erected more than ten cob houses in the Southern [[Gulf Islands]] of [[British Columbia]], [[Canada]].{{citation needed|date=July 2016}}

In 2010, Sota Construction Services in [[Pittsburgh]], [[Pennsylvania]], [[United States]], completed construction on its new 7,500 square foot corporate headquarters,<ref>{{cite web |url=http://www.sotaconstruction.com/project_details.asp?id=42 |title=Sota Construction Services, Inc. - Sota Construction Corporate Offices |access-date=2013-11-28 |url-status=dead |archive-url=https://web.archive.org/web/20131017204416/http://www.sotaconstruction.com/project_details.asp?id=42 |archive-date=2013-10-17 }}</ref> which featured exterior cob walls along with other energy saving features like [[radiant heat]] flooring, a rooftop [[solar panel]] array, and [[Daylighting (architecture)|daylighting]]. The cob walls, in conjunction with the other sustainable features, enabled the edifice to earn a [[Leadership in Energy and Environmental Design|LEED]] Platinum rating in 2012, and it also received one of the highest scores by percentage of total points earned in any LEED category.<ref>{{Cite web|url=http://www.usgbc.org/projects/sota-construction-office-expansion|title = Sota Construction Office Expansion &#124; U.S. Green Building Council}}</ref>

In 2007, Ann and Gord Baird began constructing a two-storey cob house in [[Victoria, British Columbia|Victoria]], [[British Columbia]], [[Canada]], for an estimated $210,000 CDN.  The home of 2,150 square feet includes heated floors, solar panels, and a southern exposure to enable [[passive solar heating]].<ref name="Indy2">{{cite news|url=https://www.theglobeandmail.com/life/a-dream-home-made-of-mud/article1079750/|title=A Dream Home Made of Mud|last=Barton|first=Adriana|date=3 August 2007|newspaper=[[The Globe and Mail]]|access-date=2008-09-26}}</ref>

Welsh architect [[Ianto Evans]] and researcher Linda Smiley refined the construction technique known as "Oregon Cob" in the 1980s and 1990s. Oregon Cob integrates the variation of wall layup technique which uses loaves of mud mixed with sand and straw with a rounded architectural stylism.<ref>[http://www.networkearth.org/naturalbuilding/history.html The History of Cob]</ref><ref>[http://www.alternativesmagazine.com/17/kemery.html Building with Oregon Cob]</ref> They are experimenting with a mixture of cob and straw bale denominated "[[balecob]]".

==Cob building code==
In 2019 an appendix for the International Residential Code (IRC) was approved by a vote in the public comment hearings.<ref>[https://www.iccsafe.org/building-safety-journal/bsj-technical/cob-code-appendix-approved-for-the-2021-irc/ Cob code appendix approved for the 2021 IRC]</ref> Appendix U of the IRC governs use of cob in load-bearing walls of single story residential structures. Based on currently available test data, the appendix limits the conditions under which cob may be used without engineering approval, such as seismic activity.
==See also==

{{div col|colwidth=48em}}
* {{annotated link|Adobe}}
* {{annotated link|Appropriate technology}}
* {{annotated link|ARGE-SH}}, a German Research-Institute for Cob-buildings
* {{annotated link|Chirpici}} (a variant of cob used in southern Romania)
* {{annotated link|Composite material}}, the earliest human-made composite materials were straw, combined with mud, to make bricks and walls.
* {{annotated link|Compressed earth block}}
* {{annotated link|Earth structure}}
* {{annotated link|Earthbag construction}}
* {{annotated link|LOHAS}}
* {{annotated link|Mudbrick}}
* {{annotated link|Rammed earth}}
* {{annotated link|Rice-hull bagwall construction}}
* {{annotated link|Sod}}
* {{annotated link|Sod house}}
* {{annotated link|Straw-bale construction}}
* {{annotated link|Superadobe}}
* {{annotated link|Vernacular architecture}}
* {{annotated link|Woodway House}}, a typical Devon cob building
{{div col end}}

== References ==
{{Reflist}}

==Further reading==
* ''Building With Cob, A Step by Step Guide'' by Adam Weismann and Katy Bryce. Published by Green Books ; 2006, {{ISBN|1-903998-72-7}}.
* ''The Hand-Sculpted House: A Philosophical and Practical Guide to Building a Cob Cottage'' (The Real Goods Solar Living Book) by Ianto Evans, Michael G. Smith, Linda Smiley, Deanne Bednar (Illustrator), Chelsea Green Publishing Company; (June 2002), {{ISBN|1-890132-34-9}}.
* ''The Cob Builders Handbook: You Can Hand-Sculpt Your Own Home'' by Becky Bee, Groundworks, 1997 {{ISBN|978-0-9659082-0-7}}

* ''Essential Cob Construction: A Guide to Design, Engineering, and Building'' by Anthony Dente PE, Michael Smith, and Massey Burke, New Publishers Society; 2024, ISBN 978-0865719682. 

==External links==
{{Commons category|Cob (building material)}}
* [https://web.archive.org/web/20231217000925/https://weblife.org/cob/ The Cob Builders Handbook]
* [http://pinkbird.org/w/How_to_construct_a_pizza_oven_dome_out_of_cob How to Build a Traditional Cob Oven]

{{Authority control}}

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[[Category:Sustainable building]]
[[Category:Appropriate technology]]
[[Category:Natural materials]]
[[Category:Rammed earth]]
[[Category:Soil-based building materials]]
[[Category:Sustainable products]]
[[Category:Clay]]